1. Field
The present invention relates generally to data communications, and more specifically to preamble miss detection in communication systems using Automatic Repeat Request (ARQ) processes.
2. Background
A CDMA system may be designed to support one or more CDMA standards, such as (1) the “TIA/EIA-95 Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System” (this standard with its enhanced revisions A and B will be referred to as the IS-95 standard), (2) the “TIA/EIA-98-C Recommended Minimum Standard for Dual-Mode Wideband Spread Spectrum Cellular Mobile Station” (the IS-98 standard), (3) the standard sponsored by a consortium named “3rd Generation Partnership Project” (3GPP) and embodied in a set of documents including Document Nos. 3G TS 25.211, 3G TS 25.212, 3G TS 25.213, and 3G TS 25.214 (the W-CDMA standard), (4) the standard sponsored by a consortium named “3rd Generation Partnership Project 2” (3GPP2) and embodied in a set of documents including “TR-45.5 Physical Layer Standard for cdma2000 Spread Spectrum Systems,” the “C.S0005-A Upper Layer (Layer 3) Signaling Standard for cdma2000 Spread Spectrum Systems,” (5) the “TIA/EIA/IS-856 cdma2000 High Rate Packet Data Air Interface Specification” (the cdma2000 1xEV-DO standard), and (6) certain other standards.
Examples CDMA communication systems are described in U.S. Pat. No. 4,901,307, entitled “Spread Spectrum Multiple Access Communication System Using Satellite or Terrestrial Repeaters,” and in U.S. Pat. No. 5,103,459, entitled “System and Method for Generating Signal Waveforms in a CDMA Cellular Telephone System.” Both patents are assigned to the assignee of the present invention and are incorporated herein by reference.
For example, a data packet may include, in addition to the information or payload bits, one or more parity bits, Cyclic Redundancy Check (CRC) bits, checksum bits, or a combination of such bits. These error-checking bits are calculated prior to transmission based on the information-carrying portion of the packet, such as payload and preamble, and then added to the packet. On the receiving end, error-detecting bits are recalculated based on the received information, and compared to the received error-checking bits to verify integrity of the packet.
To allow reconstruction of data that has been partially corrupted or lost during transmission, convolutional codes may be used to encode the data prior to transmission. Hamming and Reed-Solomon codes are examples of such codes. Convolutional encoding typically entails transforming a segment of k0 symbols of an information frame or packet into a codeword of n0 symbols. Because k0<n0, encoding introduces redundancy into the transmitted data. The receiver may use the redundancy to reconstruct lost or corrupted symbols in the process of packet decoding, subject to various constraints. Decoders of convolutional codes include the Viterbi algorithm decoders and sequential decoders. Redundancy may also be introduced directly into the transmitted data stream through symbol repetition. Furthermore, information symbols may be interleaved in the transmitted data to spread out adjacent symbols, so that the receiver would be more likely to reconstruct data received with burst errors. Turbo codes, block codes, and other techniques may also be used for forward error correction.
For example, a packet may be divided into subpackets that are sent through a transmission channel in separate time slots. Because of redundant encoding, the information carried by the packet may be decoded from fewer than all subpackets of the packet. In some encoding schemes, the entire packet may be decoded from a single subpacket.
This situation may occur, for example, when the receiver cannot decode the packet's preamble, which is included in the first subpacket and identifies the intended receiver.